Flying RC Airplanes: The 2.4 GHz Spread Spectrum Revolution

More than innovations, recent advances in radio control technology amount to a virtual revolution in the hobby of flying RC airplanes and helicopters. While older, narrowband systems of signal transmission still have their adherents, it is clear that spread spectrum modulation will soon be the radio system of choice for those who fly RC airplanes. This article will explain briefly and in non-technical terms how the new 2.4 GHz systems differ from older methods of transmission, and why spread spectrum trumps narrowband for RC airplane and helicopters.

Traditional narrowband systems like AM (amplitude modulation), FM (frequency modulation) and PCM (pulse code modulation) must operate on specific frequencies within the 27 to 75 MHz bandwidth, with most fliers using the 72 and 75 MGz range. When flying RC airplanes, pilots in the same vicinity have to be on separate frequencies. If they’re not, signals from one transmitter will interfere with signals from the other and one flier will lose control of his aircraft, frequently resulting in a costly crash. Frequency checkers and frequency boards at flying field help prevent pilots from accidentally using causing interference, but with more and more people flying RC airplanes, and the limited number of frequencies available within the 72 and 75 MHz range, there’s always the possibility that someone will try to fly on a frequency already in use.

Spread spectrum modulation rules out the possibility of signal interference altogether by employing a wider range of the radio band. The most popular methods of 2.4 GHz transmission are Direct Sequence Spread Spectrum (DSSS) and Frequency Hopping Spread Spectrum (FHSS)—both systems do an admirable job of eliminating interference but use different technologies to do so. DSSS utilizes a unique code sequence and transmits radio waves over a wide range of a specific frequency, while FHSS operates on a narrower band and jumps or “hops” signals between numerous channels every few milliseconds. In addition to removing frequency control as a concern for anyone flying RC airplanes, both DSSS and FHSS also boost servo response time. As the servos dictate how the plane or copter moves and handles, quicker response time comes in very handy and is especially important if you’re into aerobatics or 3D flying. Plus, because they use less current than do narrowband radios, 2.4 GHz systems will also give you longer battery life and let you spend more time in the air.

If you’re still using narrowband, but have been thinking of upgrading your radio system, or if you’re just getting started flying RC airplanes, I’d recommend you take a serious look at 2.4. Spectrum and JR use DSSS, while Futaba and Airtronics 2.4 sets employ FHSS technology--all 4 manufacturers offer good quality radio control systems. Once you try 2.4, you’ll never want to go back to your old radio rig. Good (and safe) flying!

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